(A) Field of the Invention
The present invention is related to a data slice signal generation method and apparatus for an optical disk drive, and more specifically to a data slice signal generation method and apparatus for an optical disk drive applied to a Digital Video Disc-Random Access Memory (DVD-RAM) disk.
(B) Description of the Related Art
Because of the characteristics of the design on DVD-RAM disk, the header areas and the data areas, or namely the user data areas, are made of different materials for recording addresses and data, respectively. The header areas, also called the embossed fields, are evenly distributed on the disk. Both the above-described two areas have different optical reflectivity owing to the different materials, inducing the generated radio frequency (RF) signal when the optical pickup head of the optical disk drive reads data that has an offset between different areas, as shown in FIG. 1(a). As shown in FIG. 1(b), the central line, i.e., central voltage, between the crest and the trough of a wave of an RF signal is hereinafter defined as the central level.
For digitization, a central level signal or namely data slice signal is used for crosscutting the RF signal, the parts larger than the data slice signal are “1,” and the others are “0.” The data slice signal is adjusted according to the fluctuation of the RF signal and in an attempt to approach the centers of the waves of the RF signal, i.e., the central levels of the waves of the RF signal, by one wave after another. However, because of the offset of the RF signal in the header area and the data area, it is hard to timely adjust the data slice signal to the center of the RF signal wave after changing areas, i.e., the response of the data slice signal will lag behind the RF signal. If the data slice signal deviates from the center of the RF signal wave, the decoding error will occur easily.
Referring to FIG. 2, the header area can be divided into headers 1, 2 and headers 3, 4, where the headers 1, 2 and the headers 3, 4 are adjacent to the different sides of a track. Therefore, if the optical pickup head inclines slightly, it is possible that the RF signal has an offset between the headers 1, 2 and headers 3, 4. Besides the block “data” for data storage, the data area also includes data format blocks such as “Mirror,” “Gap,” “Guard1,” “VFO3,” “PS,” “PA3,” “Guard2” and “buffer” that are defined by the DVD-RAM specification.
Referring to FIG. 3, each header can be further subdivided into multiple sub-areas. For example, the header 1 includes the address format blocks such as “VFO1,” “AM,” “PID1,” “IED1” and “PA1” that are defined by the DVD-RAM specification.
Traditionally, the data slice signal is obtained according to the central level of previous RF signal wave. This method will not cause problems to the disk of same material such as a CD-ROM or DVD-ROM disk. However, the surface of a DVD-RAM disk has different reflectivities because of the mixture of the header areas and the data areas. Accordingly, the method cannot timely and precisely figure out the central level of the RF signal after changing area, so the probability of decoding error occurrence will be greatly increased.